Various processes have heretofore been proposed and employed in order to attain vinyl plastisol resins with high plasticizer capacity and having increased flexibility, workability and distensibility. Chief among these processes have been the customary emulsion polymerization processes. In emulsion polymerization of vinyl and vinylidene halides to make polymers and copolymers thereof, relatively large quantities of soap are employed which leads to difficulties in processing the finished dispersion or paste vinyl resins.
In emulsion polymerization, the finished product formed is a polymer latex which, theoretically, can be coagulated and remove the polymer particles which then can be dried. Hoever, this is extremely difficult to do without forming agglomerates of polymer which cannot be disintegrated. Further, these agglomerates are excessively large and detract from the usefulness of the resin when subsequently making vinyl resin plastisols. As a result, it has been the common practice in the industry to take the latex having polymer particles of the proper size and spray-dry the entire materials. However, this procedure presents problems, one of which is that when spray-drying, all of the emulsifier or soap, initially added to the polymerization mixture, is deposited on the polymer particles. The large quantity of soap so deposited usually shows up as a cloudiness, or a turbidity, when the resin or polymer is fused with a plasticizer in making a plastisol. Also, the large amount of soap present adversely affects the viscosity of the plastisol in that it produces a higher yield value than that desired. Further, the heat stability of the plastisol is affected by the soap since the same discolors at processing temperatures producing off-colored products.
Many attempts have heretofore been made to remove the soap from vinyl dispersion resins by simple washing but all of these have run into various kinds of technical problems. Various technical solutions have been proposed to solve this problem but most all have been expensive and complicated that as a result, the resin so produced was no longer competitive in the market place. As a result, little has been done to remove the soap after the spray-drying operation. Attempts have also been made to lower the soap content in the polymerization recipe but a high soap concentration is necessary in order to give the polymer latex stability and to prevent agglomeration.
In addition to the above problems in making vinyl plastisol resins by the emulsion polymerization technique, another frustrating and detrimental problem in the commercial production of polymers and copolymers of vinyl and vinylidene halides, when polymerized alone or with the other vinylidene monomers having a terminal CH.sub.2 .dbd.C&lt; group, is the formation of undesirable polymer buildup on the inner surfaces of the reactor. This deposit or buildup of polymer on said reactor surfaces not only interferes with heat transfer but also decreases productivity and adversely affects polymer quality, such as producing finer particles than desired with the resultant adverse effect on plastisol viscosity. Obviously, this polymer buildup must be removed. If not, more polymer buildup occurs rapidly on that already present resulting in a hard, insoluble crust which is extremely difficult to remove without a manual scraping operation. It would be desirable, of course, to have an emulsion polymerization process in which polymer buildup does not occur. Unfortunately, none of the known emulsion polymerization processes are capable of solving this problem completely, as well as the other problems reiterated above. There is a definite need in the art for a polymerization process via the emulsion route which meets all of these criteria.